Chemical recording of flow patterns

ABSTRACT

The flow pattern of a fluid over a surface can be determined by treating the surface to form a reactive layer, entraining in the fluid a reagent compound which is capable of chemically changing the reactive layer, and then passing the fluid over the reactive layer which is to be examined. This method is illustrated by treating an aluminum surface of a blade member (such as that in a vacuum cleaner blower) or adjacent structural members to form a thin aluminum oxide film by anodic treatment. The microporous film which is formed is then impregnated with an organic dye. An air stream containing a reactive substance, such as acid vapors, is passed over the treated blade member. The acid vapors react with the dye and/or the oxide layer and produce a visible pattern upon the blade which is characteristic of the boundary layer flow of the air stream. An examination of the visible pattern is of assistance in determining the proper design and operating characteristics of the blade. The visible pattern may be formed or preserved by chemical post-treatment, such as etching to leach out dye from unreacted portions of the layer and to provide a more permanent record for subsequent use. Alternatively, the microporous aluminum oxide layer can be treated with a fluid stream containing a reactive substance to characteristically change the layer, followed by treatment with a dye to form the visible pattern of the boundary flow.

United States Patent 1 Do'tzer et al.

[ June 24, 1975 CHEMICAL RECORDING OF FLOW PATTERNS [75 Inventors: Richard D'dtzer; Winfried Plundrich,

both of Nurnberg, Germany [73] Assignee: Siemens Aktiengesellschaft, Munich,

- Germany [22] Filed: July 7, 1972 [21] Appl. No.: 269,746

[30] Foreign Application Priority Data July 7, l97l Germany 2133835 [52] US. Cl. 73/147; 346/1; 346/135 [51] Int. Cl. G01m 9/00 [58] Field of Search 73/147, 168; 346/1, 135; 23/253 TP ['5 6] References Cited UNITED STATES PATENTS 3,753,652 8/1973 Gassman et al 23/253 TP Primary Examiner-S. Clement Swisher Attorney, Agent, or Firml(enyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT The flow pattern of a fluid over a surface can be determined by treating the surface to form a reactive layer, entraining in the fluid a reagent compound which is capable of chemically changing the reactive layer, and then passing the fluid over the reactive layer which is to be examined. This method is illustrated by treating an aluminum surface of a blade member (such as that in a vacuum cleaner blower) or adjacent structural members to form a thin aluminum oxide film by anodic treatment. The microporous film which is formed is then impregnated with an organic dye. An air stream containing a reactive substance, such as acid vapors, is passed over the treated blade member. The acid vapors react with the dye and/or the oxide layer and produce a visible pattern upon the blade which is characteristic of the boundary layer flow of the air stream. An examination of the visible pattern is of assistance in determining the proper design and operating characteristics of the blade. The visible pattern may be formed or preserved by chemical post-treatment, such as etching to leach out dye from unreacted portions of the layer and to provide a more permanent record for subsequent use. Alternatively, the microporous aluminum oxide layer can be treated with a fluid stream containing a reactive substance to characteristically change the layer, followed by treatment with a dye to form the visible pattern of the boundary flow.

12 Claims, 12 Drawing Figures PATENTED JUN 24 I975 SHEET CHEMICAL RECORDING OF FLOW PATTERNS BACKGROUND This invention is directed to the art of determining and recording the flow characteristics of a fluid past a surface. For example, in blowers (such as vacuum cleaners) it is desirable to provide devices with a minimum power consumption. a maximum suction or output capacity. and a minimum noise level. The power consumption, suction capacity and noise level of a blower are closely interrelated and depend directly on each other; more power produces more suction capacity, and higher suction capacity leads in most cases to an increase in the noise level. In the last analysis the objective of design efforts is an optimization of the blower characteristics by modification and compromise between the various parameters.

In optimizing the blower design, however, exact information is required regarding the flow conditions in the blower and at the sources of noise generation. Mathematical solutions are too difficult and require too much effort. Purely physical efforts involving the stroboscopic-photographic determination of the trajectories of light particles of plastic sprinkled into the air stream have not been successful.

Therefore a need exists for a technique to analyze the flow conditions. particularly the flow pattern of fluids over surfaces of rotors, guide vane rings, blades, airfoils and adjacent structural members and housings for a wide variety of devices, such as the vacuum cleaner blower referred to above. As far as possible, such a method should be applicable to the actual surface, and it should be possible to record the existing flow conditions without interference and in a reproducible manner.

Accordingly, it is an object of this invention to provide improved techniques and devices for chemically recording the flow pattern of a fluid over a surface. This, and additional objects, and the manner of achieving them, are set forth more fully in the following detailed specification.

THE INVENTION This invention is directed to treating a reactive surface with a fluid containing a reagent which interacts with the reactive surface; a dye substance added to the reactive surface prior to, or after contact of the surface with the fluid, provides a visible record of the flow pattern of the fluid over the surface.

It has been found that the recording of a boundary layer flow by chemical means is made possible if an anodically oxidized surface (referred to herein as the formation of an eloxal layer) is exposed (in an unsealed condition) to an air stream mixed with reactive acid, alkaline or gaseous chemical reagents, and the eloxal layer which is differentially altered by the gas stream, is dyed (or stained).

It has also been noted that the eloxal layer and the dye that may be present undergo characteristic changes which are dependent on the local concentration of the reagent in the fluid. As the local concentration of the reagent conforms to the air compression in the flow profile, the chemical reagent records the flow pattern of the boundary layer flow very accurately on the eloxal layer, almost with molecular resolution. This process can thus be termed a method of chemically recording flow patterns of boundary layer flow. The process is referred to herein as chemical recording (or chemigraphy), and the records obtained are called chemigraphs (or chemical recordings). Very highcontrast chemigraphs can be obtained in color, or in several colors. they are referred to as eloxal-colorlayer chemigraphs."

The eloxal layer is illustrative of the type of microporous layer which is preferred. The microporous layer can be impregnated with a dye to produce a visible recording of the flow layer upon treatment with a fluid containing a dye-reactive reagent or a reagent which seals the pores of the layer followed by leaching of the unsealed dye. Alternatively an undyed microporous layer can first be treated with a reagent which reacts with the microporous layer to selectively seal its pores and then a dye can be used to produce a visible pattern of the fluid flow. The microporous eloxal layer is preferred, but other microporous oxides or synthetic layers may be used.

The method of this invention is particularly suited for the recording of steady-state flow conditions in blowers. It allows the recording of existing flow conditions (flow profiles) directly, unaltered and reproducibly on the portions of the surfaces which are contacted by the air flow. Thus the air stream records itself on the adjoining surface portions of the parts of the blower.

The following figures further illustrate the present invention.

FIG. 1 shows the chemical recording of the boundary layer flow of a radial rotor with straight, centrically or radially. respectively. arranged blades.

FIG. 2 shows the chemical recordings of a so-called parallel-blade rotor with blades curved in sicklefashion.

FIGS. 3, 4 and 5 show chemical eloxal-red-layer recordings, of the first rotor of the blower, recorded at 30% output of the blower motor and contrast-etched by means of sodium hydroxide. FIG. 3 shows the base plate and FIG. 4, the cover plate. The concave side of the curved, sickle-shaped blade is shown in FIG. 5.

FIGS. 6 to 11 show chemical recordings of the boundary layer flow of different aerodynamic bodies on small eloxal-dye-layer base plates.

FIG. 12 shows a boundary flow layer of air directed at an angle against a sheet member.

FIGS. 1 and 2 show in each case the inside surface of the lower circular disc (base plate) of the first rotor wheel of a two-stage blower and show clearly the contact edges of the removed blades. Both rotors were in rotation during the chemical recording in a clockwise direction, at a speed of rotationof the blower of 12,000 rpm. They were discolored in a manner characteristic of the flow.

The areas appearing dark in the figures indicate clearly the pattern of the air flow; the lighter portions of the area are regions of under-pressure which are hardly touched by the air stream. From the flow shadows of the three central attachment straps (in the experiment, the two circular discs of the rotor were held together by six bolted straps in order to make it unnecessary to cut the blades, which are also chemically recorded), the main direction of the flow can be seen particularly clearly in FIG. 1. A comparison of the two chemical recordings discloses clear fundamental differences in the pattern of the boundary layer flows.

The method according to this invention is particularly well suited for making visible the boundary layer flow of moving fluid media, particularly of air. gases and vapors of high flow velocity. such as they appear in parts of blowers. It is used to advantage for the recording of flow profiles in the rotors, stators and housings of vacuum cleaner blowers, rotary flow dust separators, counter-jet pulverizers and cyclone separators. The method designated herein as chemigraphic recording of boundary layer flow provides very durable. high-contrast flow patterns (chemigraphs). With appropriate pre-treatment of the surfaces it can also be applied to parts which do not consist of aluminum material. By evaluating the chemigraphs of the surface portions adjoining the flowing fluid. informative insights can be obtained into the spatial flow processes.

Numerous reagents can be readily and uniformly encorporated in a fluid medium to react with and modify the color of a dye in an eloxal layer. Strong acids and bases, and reactive gases are suitable.

Nitric acid vapors can be added as the chemical reagent to the air stream, and one can record chemically for eight minutes or longer, if required. The chemographic recording then shows immediately the contrast reproduced in the image and is very durable. Ozone also can be added advantageously to the air stream as the chemical reagent. As almost all aluminum dyes are by oxidation decomposed, i.e., modified or destroyed and thereby bleached, full-range chemical recordings can be obtained in a few minutes with an oxonecontaining air stream. With somewhat higher ozone concentrations, fractions of a minute are sufficient. For example. the chemical recording of a red eloxal layer with an acid produces a stronger color hue in the area of contact whereas the ozone-containing air stream records the flow patterns as lighter to colorless areas on the dyed eloxal layer background. The reproducibility of these chemical recordings is very good, as the amount of ozone can be fixed and apportioned exactly by means of the accurately adjustable control parameters of conventional ozone generators.

It has also been found advantageous in some cases, to use an eloxadized, unsealed and undyed surface of a blower component. This technique is useful because not only can the aluminum dye be altered, but the eloxal layer can also be specifically influenced by the chemical reagent. In carrying out this method, a surface can be chemically recorded for several minutes with a fluid containing nitric acid vapors (or with hydrogen chloride mist). Then, if desired, the parts can be left at room temperature for several hours, i.e., about 8 hours for a setting of the chemically recorded layer, and subsequently placed in a dye bath for about 10 minutes. After rinsing with water, the chemical recordings are finished. The portions not contacted by the air stream, which therefore have not been chemically recorded, will have absorbed dye and thereby are clearly distinguished from the colorless chemically recorded boundary layer flow areas.

Thus, the reagent in the fluid can be of different functional types. one which reacts with the dye in the eloxal layer to change the color of the dye, or which reacts with the eloxal layer to seal its ports, or a combination of such reactions. The choice of reagent can be readily made from those known to react with dyes and/or to seal microporous structures such as an eloxal layer.

A further, particularly advantageous embodiment is to chemically post-treat the eloxal layer which is differentially altered by the method of this invention. In the case of chemical eloxal-dye-layer recording. this process is called contrast etching. A reduction of the exposure time is thereby achieved (to 3 to 5 minutes) and a chemigraph of even higher contrast is obtained, as is shown in FIGS. 3 to 5.

The flow profiles on the base plate (FIG. 3) as well as those on the inside of the cover plate (FIG. 4) can be seen most clearly. Even before the chemigraphic reaction between the chemical reagent and the eloxaldye layer becomes optically visible as a color differentiation, the chemical reagent has changed the structure of the eloxal layer and the dye so that the chemically recorded portions of the surface show a considerably more resistant behavior than the areas which have been exposed less or not at all.

For contrast etching, practically any aluminum dyes can be used, although the strongly dyed basic colors red, yellow and blue (and as a mixed color, green) are preferred because they provide sharp contours and clear contrast. I

The chemical post-treatment can be a brief etching, which can be performed with acids as well as with alkaline solutions. The more easily and rapidly the dye can be locally dissolved, the less the eloxal dye layer has been exposed in the chemical recording, i.e., the less its state has been changed. Immersion times of between 5 and 30 seconds are sufficient for the etching process; with immersion times of over five minutes fuller decomposition of the chemigraphic image will occur. If sodium hydroxide is used, immersion times of less than 5 seconds are sufficient. For 20% sodium hydroxide, for instance. an immersion time of three seconds has been found suitable. Immediately after the etching operation the surface is rinsed liberally with Water and finally dried between filter paper.

Other etching media which have been found are concentrated aqueous ammonia and particularly, nitric acid and sulfuric acid with the immersion times mentioned above. It has been found advantageous to chemically record and contrast-etch with the same acid. The chemical recording is perferably done with nitric acid vapor, and this acid is then used for the contrast etching. A concentration of about 65% acid produces clear contrast between the chemically recorded eloxal-dye- ]ayer areas and the colorless parts of the surface which have not been exposed.

While alkaline solutions attack the eloxal layer structure for chemical reasons, this is not directly the case with the acid etching media. However, they dissolve the aluminum dye very rapidly from the chemically recorded aloxal-dye-layer areas and apparently do not alter the structure of the eloxal layer. Thus, the eloxal layer areas relieved of dye in the contrast etching can be dyed again. It is advantageous to use an aluminum dye which contrasts with the dye first used. as for instance:

lst dyeing operation 2nd dyeing operation red blue yellow blue red black yellow black l yellow The chemically recorded eloxal-dye-layer areas of the first dyeing operation are not altered in the second dyeing operation. Only in the partially chemically recorded border zones of the flow are they dyed proportionally. This color contrasting in chemical recording constitutes a further refinement. It can furnish additional information regarding the flow pattern in the border zones.

The etching technique is also useful where the reagent in the fluid does not visibly change the color of the dye. Thus the reagent may only serve to seal the microporous structure of a dyed eloxal layer at characteristic areas of the boundary flow layer. Upon etching of leaching the dye is removed from the unsealed areas to provide a visible pattern.

The dyeing of the aluminium layer can preferably by carried out with two or more aluminium dyes. The con trast of the chemical recording is thereby enhanced.

Almost the entire spectrum of the so-called aluminium dyes (or stains) offered commercially for the dyeing of eloxal layers can be used for the chemigraphic recording of boundary layer flow, for example Alizarinlndigo-, Azo-, Cotton-, Metal-Complex-dyestuffs according to B. S. WERNICK and R. PINNER handbook The Surface Treatment and Finishing of Aluminium and its Alloys third edition, in German Die Oberflachenbehandlung von Aluminium page 367369.

The microscopic depressions existing in the eloxal layer are first filled partially with the one dye, and then partially with the other dyes. They may, for instance. first be filled with a blue dye and then on top with a yellow dye. The resulting color effect is green. In chemical recording, the yellow dye is partially altered or decomposed. respectively, and at other points, all dyes are affected, depending on the concentration of the chemical reagent caused by the flow. Thus a flow pattern differentiated by green-blue-colorless is obtained.

The chemical recording sensitivity of the eloxal dye layer can be reduced by partial sealing of the microscopic depressions. To lock the dye in the eloxal layer, the surface can be sealed in boiling water for minutes to 1 hour.

Eloxal-red-layer chemigraphs have been found to be excellent on the basis of their color contrast, which can be obtained by dyeing the eloxal layer with a red dye, and sealing and exposing with nitric acid-containing vapors.

Suitable red dyes are, for instance, the following:

Aluminium True red B 3 LW Aluminium dark red LW Aluminium ruby B LLW Aluminium red RLW Aluminium red GLW Aluminium true gold Aluminium blue LLW Aluminium green GLW Aluminium true bronze L Aluminium copper 2 RLW Aluminium orange GL Aluminium gold yellow GLW Aluminium true blue G Aluminium purple BLLW Aluminium turquoise PLW Aluminium red brown RLLW With the chemigraphic reagent ozone, indigo and its derivates are particularly well suited as are Redox indicator dyes such as, for instance, methylene blue, Congo red, toluylene blue, thiazine, safranin T, and neutral red. Furthermore, dyes which change by oxidation in air have been proven highly suitable. Steamvapors can also be used as the chemical reagent to react with the dyeable substance or eloxal layer.

The reagent compound. in vaporous or gaseous form. is readily dispersed in and mixed with the fluid stream by conventional means. The fluid stream may be passed over a vat of rising vapors or a gas generator can direct reagent gases or vapor into the fluid stream. A baffle network or mixing device may be used if desired to ensure even dispersion of the reagent in the fluid stream.

The eloxal layers prepared by customary methods through anodic oxidation of the surface are suitable for carrying out the method of this invention. The wellknown d-c sulfuric acid method (GS method) is the most widely employed and most inexpensive process for the anodic oxidation of aluminum and aluminum alloys. The eloxal layers produced thereby have a microporous or honeycomb-like fine structure. These non-conducting, mechanically strong surfaces are particularly resistant against atmospheric influences and accept dye very well. When dyeing with commercially available aluminum dyes, for instance, those marketed by the firm Sandoz, AG, Basle, Switzerland, the dye molecules (mostly organic azo dyes) are impregnated into the microscopic depressions of the eloxal layer, which are about A in diameter and about l0 ,um depth. The dye is therefore not on the surface but in the eloxal layer and is not carried away by gas even of very high flow velocities. At the same time the eloxal surface presents a very homogenous and, if required, even polishable surface, which does not interfere with the flowing media. It is also thermally stable.

Alternative methods of forming an eloxal-type coating can also beused. For example commercial coating are also made by treating the aluminum in an electrolyte of chromic acid, oxalic acid, or oxalic acid mixed with sulfuric acid. Artificial oxide coatings can be formed in aluminum articles by chemical treatment as well as by electrochemical treatment. These chemical coatings are not as thick or as hard nor as abrasionresistant as anodic coatings, but for many purposes they are adequate.

The chemigraphic recordings can be made of practically unlimited durability by sealing after the chemigraphic exposure. This can be accomplished; for instance, by sealing for 30 minutes in boiling water or in a commercially available sealing salt bath.

The original chemigraphs obtained by the method of this invention can be preserved by means of photography in color or in black and white. For comparison purposes the photographs can also be evaluated quantitatively by means of photometry. The chemigraphs can also be used as standards of proper flow patterns for purposes of matching new blade or structural units with a known standard of a flow pattern that has proven to be effective.

The eloxal layer may consist of an anodically oxidized. surface of an aluminum part. A particularly advantageous embodiment of the method according to the invention is based on the use of a self-adhering eloxadized aluminum foil. In many cases it may be found to be particularly advantageous to dye the eloxal layer.

If the part to be tested is not made of aluminum, or does not have an aluminum surface, an aluminum foil or sheet coated with an eloxal dye layer can be cemented on to the surface of the part or equipment for carrying out the method of this invention. A test piece can also be aluminum-plated by electro-deposition and subsequently eloxadized. Rotors or blowers of brass or sheet steel can, for instance, be aluminum-plated by electroplating, eloxadized and then dyed and chemically recorded on by the method of this invention.

By using an eloxadized aluminum foil, the method according to this invention becomes practically independent of the kind of material of the part or equipment which is to be tested for its aerodynamic characteristics. In principle, any kind of aluminum foil is suitable. which is eloxal-coated on one or both sides, and is undyed or dyed with a suitable aluminum dye. The foils are cemented to the surface portions of the part or equipment which is of interest from a flow point of view, and the boundary layer flow profiles are recorded by the method according to this invention. The impregnated paper-laminated, self-adhering aluminum foil, which is commercially available in sheet form or as yard goods, is particularly well suited for carrying out the method described herein. The foil is cut to conform to the surface portions to be tested by chemical recording and affixed to the surface of the object with its adhesive side. After the chemical recording, the selfadhering foil, which has the flow profiles recorded in the dyed eloxal layer, can be stripped off the surface. The foil can be preserved for purposes or comparison or documentatiomand can be mounted on a rigid support, such as cardboard, for ease of handling.

Particular advantages of this embodiment are seen, for instance, in the fact that the self-adhering eloxaldye-layer aluminum foil is applicable regardless of the base material of the part or equipment to be chemically recorded. The use of such foil furthermore makes the method independent of anodizing and dyeing equipment, and it can be used at any location. The boundary layer flow at given portions of the surface of parts or equipment can be chemically recorded with different foil pieces as many times as desired under different flow conditions and can be compared very well visually by juxtaposition of the chemical recordings on the foil pieces and evaluated with respect to changes that may have occured.

In particular, the self-adhering eloxal-dye-layer aluminum foils can be cemented on non-planar, convexor concave-cylindrical surfaces or differently shaped surface portions, and the chemically recorded parts of the foils can be cemented side-by-side on flat cardboard for comparison purposes. The foil also offers the possibility to investigate, on the basis of different aluminum dyes and chemical recording reagents, the surface areas of interest under the same flow conditions by means of chemical recording methods which record with different speed and resolution, and so to obtain more information regarding the flow process. For example an eloxal layer can be formed with an acidreactive dye and basic-reactive dye(or more generally, two or more dyes which are subject to distinguishable visible changes at different pHs). A first flow condition can then be established with a fluid containing an acid entrained therein and subsequently a second flow condition (i.e. a faster rate) can be established with the fluid containing a base entrained therein. This leads to a single eloxal layer containing two distinguishable patterns which reflect the changes in boundary layer flow caused by the different flow conditions.

In order to protect the exposed (unsealed) and therefore dirt-sensitive eloxal-dye layers against contamination and modifying influences, it may be advisable to cover them with a removable protective foil. This 'is recommended particularly if the self-adhering eloxaldye layer foil is to be stored for an extended period of time. Inthe case of sheets and yard goods, the insertion of an inertsheet, for instance, a commercially available thin polyethylene foil, is sufficient for this purpose.

The invention will be explained more fully by the following examples:

EXAMPLE I A l-mm thick sheet of Raffinal (a high-purity aluminum sheet), which had eloxadized to a thickness of about ,um by the GS method, was dyed for 10 minnutes at room temperature in a dye bath with an Azodyestuff like Al True Red B3LW (made by Sandoz) at a concentration of 5 g/liter. From a nozzle of 2 mm diameter (placed onn the left side) the eloxal-dye layer was exposed to an air stream of 500 liter/h at an angle of inclination of 5C. The air stream contained at the chemical reagent the vapors carried along by it from the gas space above 65-% nitric acid at room temperature. The chemical recording time was 75 seconds (approximately 50 mg of HNO The boundary layer flow pattern shown in FIG, 12 was obtained, which shows the heavily exposed inner cone and the wide outer cone, which is differentiated by its color. Although the chemigraph was not sealed, it was very durable EXAMPLE 2 According to the description in Example 1, an eloxalred-layer chemigraph was prepared, pursuant to the following specifications.

Object: P-wheel of the VS 26 vacuum cleaner blower Material: Sheet of aluminium alloy Pre-treatment: Degreased in TRINORM Al: GS

eloxation for for 30 min;

Dyeing: in a dye bath with 5 g/liter of an Azo-dyestuff like Al True Red B3LW(made by Sandoz); 10 minutes at room temp.;

Chemical reagent: 65 HNO vapors at room temperature (approx. mg of HNO .min);

Exposure time: 8 minutes at a suction rate of 32 liter/sec of air.

The eloxal-red-layer chemigraph obtained corresponds to that of FIGS. 1 and 2.

If the chemical recording exposure is only 3 to 5 minutes, a high-contrast chemigraph can also be obtained by a 3-min heat treatment at 100C in a drying cabinet, and also by contrast etching, as described above.

EXAMPLE 3 According to the description in Example 1 and using the object, material and pre-treatment of Example 1, an eloxal-blue-layer chemigraph was prepared pursuant to the following specifications.

Dyeing: 3,5 g/liter of an Indigo-dyestuff like Al Blue LLW; 10 minutes at room temperature Chemical reagent: Ozone, approximately ml of 0;,

gas to 1920 liter of air per minute:

Exposure time: 1 minute at a suction rate of 32 liter/- sec of air;

Result: Immediate chemigraph with blue-colorless contrast.

EXAMPLE 4 Accordingtothe description in Example 1 and using the object and-material, and. according to the pretreatment, of Example 1, an eloxal-yellow-layer chemigraph was prepared and contrast-etched under the following conditions:

Dyeing: 10 g/liter of an Alizarin-dyestuff like Al Yellow; 5 minutes at room temperature;

Chemical reagent: Nitric acid vapors of 65-% NI-IO at room temperature; approximately 20 mg of HNO per minute;

Exposure time: 5 minutes at a suction rate of 18.5 liter/sec of air;

Etching medium: 65-% NHO,-,:

Etching time: 5 sec, then liberal rinsing with water;

Result: Immediate chemigraph with yellow-colorless contrast.

EXAMPLE .5

Similarly as in Example 4, an eloxal-green-layer chemigraph with color contrast was prepared, using the following:

Dyeing: 3.5 g/liter of an Indigo-dyestuff like Al Blue LLW, 2.5 min at room temp.,

Chemical reagent: Nitric acid vapors of 65-% I-INO at room temperature. approximately 20 mg of HNO3 Per min;

Exposure time: 5 minutes at a suction rate of 18.5 liter/sec of air;

Etching medium: 65-% HNO Etching time: 10 sec, then liberal rinsing with water;

Dyeing: l g/liter of Al Black MLW; min at room temperature;

Result: Chemigraph with strong green-black contrast.

EXAMPLE 6 Eloxal-red-layer chemigraphs according to FIGS. 6

to 8 were obtained using the following:

Object: Aerodynamic body model (drop 1, cylinder 2, cup 3) between sheet metal surfaces (4, 5, and 6 respectively) in the flow channel. The aerodynamic bodies of the same cross section X 10 mm), exhibit different flow resistance due to their different shapes, which can be made visible chemigraphically via the width of the pressure head zone;

Material: Aluminium for the aerodynamic bodies,

Raffinal for the sheet metal pieces;

Pre-treatment: TRINORM Al degreasing; chemical burnishing; GS- eloxation for minutes;

Dyeing: in a dye bath with 5 g/liter of an Azo-dyestuff like Al True Red B3LW (made by Sandoz); 7 minutes at room temperature;

Chemical reagent: Nitric-acid vapors from 65-% HNO approximately 50 mg/min;

Exposure time: 2 min at a suction rate of 7 liter/sec of air;

Result: Chemigraphs of the boundary layer flow on the surfaces of the aerodynamic bodies and on the adjoining surfaces of the sheet metal surfaces were obtained.

EXAMPLE 7 Eloxal-red-layer chemigraph according to FIGS. 9 to 11 were obtained with material, pre-treatment, dyeing, chemical reagent and exposure time as in Example 6. The objects were a wing profile 7, triangular wedge 8 and an asymmetrical angle piece 9 as model forms between sheet metal surfaces (10, 11 and I2, respectively) in a flow channel.

Chemigraphs of boundary layer flow with dark-red contrast were obtained on the model forms and sheetmetal surfaces, which correspond to the aerodynamic expectations.

EXAMPLE 8 An eloxal-red-layer chemigraph with contrast etching was prepared by using the following.

Object: P-wheels of the VS 26 blower;

Material: Sheet steel and brass, respectively;

Pre-treatment: Aluminium-plated by electrodeposition (approx. 25 ,um of Al and eloxadized (eloxal layer about 8 am thick);

Dyeing: in a dye bath with 5 g/liter of an Azo-dyestuff like A] True Red B3LW; made by Sandoz) 8 minutes at room temperature;

Chemical reagent: Nitric acid vapors from 65-% I-INO approximately 20 mg of HNO per min;

Exposure time: 3 minutes at a suction rate of 32 liter/sec of air;

Etching medium: 65-% HNO Etching time: 10 sec, then liberally rinsing with water.

A chemigraph with red-colorless contrast was obtained as with the P-wheels made entirely of aluminium, i.e., the eloxadized and dyed electro-deposited aluminium corresponds fully to a equivalent eloxal-dye layer and accordingly produces fully equivalent'chemigraphs.

EXAMPLE 9 A chemigraph with colorless-blue contrast was prepared as follows:

Object: P-wheel of the VS-26 vacuum cleaner blower;

Material: Sheet of aluminium alloy;

Pre-treatment: Degreasing in TRINORM Al, eloxa dizing form 30 min;

Chemical reagent: Nitric acid vapors from 65-% I-INQ; at room temperature, approximately 20 mg I-INO3/min;

Exposure time: 5 minutes at a suction rate of 32 liter/sec of air;

Settling time: About 8 hours at room temperature;

Dyeing: 8 g/liter of an Indigo-dyestuff like Blue LLW;

10 minutes at room temperature;

Result: Colorless-blue chemigraph with sharp contours.

EXAMPLE 10 Similarly as in the descriptions in the preceding examples, a vacuum cleaner blower was eloxadized and chemical recordings made. The vacuum cleaner blower is a two-stage blower. Two rotor wheels, which are mounted in tandem on a shaft and are separated from each other by a stationary guide vane wheel, are driven by an electric motor. The air entering the first rotor wheel centrally is accelerated radially outward, is deflected at the housing and is fed through the guide vane wheel inward to the second rotor wheel, which accelerates the air again radially outward. The two rotor wheels have the same shape and each consist of two circular discs which are rigidly connected by six curved, sickle-shaped, radially and symmetrically arranged webs, the so-called rotor blades. With a circular disc diameter of mm, the rotor blades are 8 mm high and are riveted by means of suitable tabs firmly to the circular discs. The guide vane wheel which, with a diameter of 150 mm, is somewhat larger, looks similar, and consists likewise of two circular discs perforated in the center, which are firmly connected with each other by eight, 8 mm high guide vanes in a similar manner. The guide vanes are straight webs, symmetrical, but are not arranged centrically about the Center. The rotor wheels are fixed on the shaft of the electric motor by means of a balancing nut and can reach up to 20,000 r.p.m. The parts of the blower and the electric motor are enclosed by a housing with a cover and they constitute the vacuum cleaner blower.

The rotor wheel and the guide vane wheel are made of aluminum. The chemigraphs obtained give information regarding the parts of the blower, the influence of the shape of the blades, the inner and outer attack angle of the blades, the shape of the entrance openings and, in the last analysis, information regarding the flow distribution and noise generation in the flow spaces between the blade and disc surfaces. They make it therefore possible to optimize the blower parameters and to improve the blower efficiency without increasing the noise level.

EXAMPLE 1 l A sheet, 500 X 700 mm, of aluminum foil from JACKSTAEDT and Company, Wuppertal-E, with about 50,u.m of aluminum, with shiny aluminum surface (WI-CA 1 52125) or matte (WI-52124) and laminated on one side with adhesive and removable impregnated paper, is freed of the thin protective lacquer film applied for manufacturing reasons by means of dischloromethane. ln order to remove the last lacquer residue, the laminated aluminum foil is briefly immersed in diluted sodium hydroxide to and subsequently thoroughly rinsed in water. Any degreasing that may be necessary is done by immersion for 10 to 20 seconds in TRINORM Al (Schering).

The aluminum foil, which is laminated on one side, is then anodically oxidized in the well-known d-c sulfuric-acid GS eloxadizing bath at 18C for minutes with a current density of 1.5 A/dm at a voltage of 16 V, and an eloxal layer of 10 to 12 um thickness is produced. subsequently the aluminum foil, now coated with an eloxal layer, is washed thoroughly for 5 to 10 minutes in water and dyed red for 10 minutes at room temperature in a dye bath with an Azo-dystufflike Aluminum True Red B3LW (SANDOZ AG, Basel) at a dye concentration of 5 g/liter. After a brief rinse in distilled water, the eloxal-red-layer aluminum foil is wiped off with filter paper and is allowed to dry at room temperature in clean air. The unsealed. self-adhering aloxal-red-layer aluminum foil is now ready for the chemical recording of boundary layer flow.

The inner wall of a glass tube of 30 cm length and 10 cm side diameter is coated with the self-adhering eloxal-red-layer aluminum foil, after the calculated area was first cut out from the 500 X 700 mm sheet and the impregnated paper foil stripped off. In order not to contaminate the eloxal-red-layer in handling, it is recommended to use clean protective gloves. The boundary layer flow within the tube was determined from an air jet with a discharge orifice of 2 mm in diameter, inclined from the axis of the tube. An air stream from the jet, at a 500 liter/hr nominal flow rate, was mixed with nitric acid vapors which were carried along from the gas space over 65% HNO (approximately mg of HNO;, were fed into the air stream per minute). An exposure time of seconds (duration of the blast of air containing HNQ; vapors), was used to produce the corresponding boundary layer flow profile on the eloxal-red -layer aluminum foil within the tube.

The flow profile can be made permanently and clearly visible by removing it from the wall of the glass tube, covering the adhesive with the impregnatedpaper foil, and contrast etching the chemigraphic image. The finally sealed chemigraphic picture can then be mounted and is permanently available for evaluation and comparison.

The inside wall of the glass can be covered again with a self-adhering eloxal-red-layer aluminum foil made under the same conditions and chemigraphs can be recorded under different flow conditions.

This invention has been described in terms of specific embodiments set forth in detail. Alternative embodirnents will be apparent to those skilled in the art in view of this disclosure, and accordingly such modifications are to be contemplated within the spirit of the invention as disclosed and claimed herein.

' What is claimed is:

l. A method of chemically recording the flow pattern of a fluid over a surface which comprises:

treating said surface to produce an oxidized layer of aluminum upon said surface, passing over said layer a fluid containing a reagent compound which produces a chemical change upon contact with said layer which is characteristic of the flow pattern of the fluid over the layer, and

visibly recording said flow pattern with a dye substance in said layer.

2. The method of claim 1 wherein said dye is impregnated into said aluminum oxide layer prior to passing said fluid over said layer.

3. The method of claim 1 wherein said dye is impregnated into said aluminum oxide layer subsequent to passing said fluid over said layer.

4. The method of claim 1 wherein said reagent is a compound which reacts with said dye to change its color.

5. The method of claim 1 wherein said reagent is a compound which reacts with said aluminum oxide layer.

6. The method of claim 1 wherein the chemical change in said layer is further revealed by contacting said layer with an etching fluid.

7. The method of claim 1 wherein at least two distinguishable dyes are impregnated into said aluminum oxide.

8. The method of claim 1 wherein said treating comprises applying to said surface a self-supporting aluminum foil having on one surface an adhesive and on the opposite surface an aluminum oxide coating.

9. The method of claim 1 wherein said treating comprises electro-depositing aluminum upon said surface and treating said aluminum to form an aluminum oxide layer.

10. The method of recording the flow pattern of a gas over a surface, which comprises treating said surface to form thereon an eloxal layer containing therein an exposed dyeable substance, and

passing over said layer a gas containing a reagent which imparts a visible change to said dyeable substance.

treating said surface to form thereon a microporous eloxal layer containing therein an exposed dyeable substance.

passing over said layer a gas containing a reagent which reacts with at least said eloxal layer to seal portions of said layer, and treating said layer to at least remove said dyeable substance from the portions of said eloxal layer which are not sealed.

I; r g l t l 7 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. :3 90 835 DATED June 24, 1975 INVYENTOR(S) IRICHARD ijTZER ET A It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

in column 3, line 28, change "oxone containing" to -ozonecontaining in column 4, line 51, change "aloxal-dye-layer" to eloxal-dyelayerin column 5, line 13, change "by carried" to -be carried-- in column 8, line 11, change "which had eloxized" to wh1ch had been elmmdimd M0 in column 8, line 16, change "(placed onn)" to (placed in column 11 line 52, change "aloxal-red-layer" to eloxalredlayer Signed and Scaled this tenth D3) of February 1976 [SEAL] A ttest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner of Patents and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION I PATENT N0. 890 335 DATED :June 24: 1975 lN\/ ENTOR( IRICHARD oTZER ET AL It is certified that error appears in the above-identified patent and that said Letters Patent 0 are hereby corrected as shown below:

in column 3, line 28, change "oxone containing" to -ozonecontainingin column 4, line 51, change "aloxal-dye-layer" to eloxaldye-layer in column 5, line 13, change "by carried" to -be carried-- in column 8, line 11, change "which had eloxized" to whlch had been elmcadizad M in column 8, line 16 change (placed onn) to (placed in column 11, line 52, change "aloxal-red-layer" to -eloxalred-layer d Engnccl and Sealed this tenth Day of February 1976 [SEAL] q Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnrrrissiuner ofParems and Trademarks 

1. A METHOD OF CHEMICALLY RECORDING THE FLOW PATTERN OF A FLUID OVER A SURFACE WITH COMPRISES: TREATING SAID SURFACE TO PRODUCE AN OXIDIZED LAYER OF ALUMINUM UPON SAID SURFACE, PASSING OVER SAID LAYER A FLUID CONTAINING A REAGENT COMPOUND WHICH PRODUCES A CHEMICAL CHANGE UPON CONTACT WITH SAID LAYER WHICH IS CHARACTERISTIC OF THE FLOW PATTERN OF THE FLUID OVER THE LAYER, AND
 2. The method of claim 1 wherein said dye is impregnated into said aluminum oxide layer prior to passing said fluid over said layer.
 3. The method of claim 1 wherein said dye is impregnated into said aluminum oxide layer subsequent to passing said fluid over said layer.
 4. The method of claim 1 wherein said reagent is a compound which reacts with said dye to change its color.
 5. The method of claim 1 wherein said reagent is a compound which reacts with said aluminum oxide layer.
 6. The method of claim 1 wherein the chemical change in said layer is further revealed by contacting said layer with an etching fluid.
 7. The method of claim 1 wherein at least two distinguishable dyes are impregnated into said aluminum oxide.
 8. The method of claim 1 wherein said treating comprises applying to said surface a self-supporting aluminum foil having on one surface an adhesive and on the opposite surface an aluminum oxide coating.
 9. The method of claim 1 wherein said treating comprises electro-depositing aluminum upon said surface and treating said aluminum to form an aluminum oxide layer.
 10. The method of recording the flow pattern of a gas over a surface, which comprises treating said surface to form thereon an eloxal layer containing therein an exposed dyeable substance, and passing over said layer a gas containing a reagent which imparts a visible change to said dyeable substance.
 11. The method of recording the flow pattern of a gas over a surface, which comprises, treating said surface to form thereon an eloxal layer which is microporous, passing over said layer a gas containing a reagent which reacts with and seals portions of said layer, and contacting said layer with a dye to impregnate unsealed portions of said layer.
 12. The method of recording the flow pattern of a gas over a surface, which comprises, treating said surface to form thereon a microporous eloxal layer containing therein an exposed dyeable substance, passing over said layer a gas containing a reagent which reacts with at least said eloxal layer to seal portions of said layer, and treating said layer to at least remove said dyeable substance from the portions of said eloxal layer which are not sealed. 